Process and apparatus for refining loosely compacted refractory metals in an electron beam furnace



Apnl 28, 1964 c. w. HANKS EI'AL 3,131,051

PROCESS AND APPARATUS FOR REFINING (LOOSELY COMPACTED REFRACTORY METALSIN AN ELECTRON BEAM FURNACE Filed Sept. 23, 1959 2 Sheets-Sheet 1 April8, 1 6 c w HANKS VETAI. 3,131,051

PROCESS AND APPAR ATU S FOR REFINING LOOSELY COMPACTED REFRACTORY METALSIN AN ELECTRON BEAM FURNACE- -Filed Sept. 23, 1959 2 Sheets-Sheet 2 INVEN T0115 (Mani; (AHA/W5 0/424 55 4'4, hl A f' United States Patent3,131,051 PROCESS AND APPARATUS FOR REFINING LOOSELY C O M P A C T E DREFRACTORY METALS IN AN ELECTRON BEAM FURNACE Charles W. Hanks andCharles dA. Hunt, Orinda, Califl, assignors to Stauifer ChemicalCompany, New York, N.Y., a corporation of Delaware Filed Sept. 23, 1959,Ser. No. 841,828 2 Claims. (Cl. 7510) This invention relates to aprocess for refining loosely compacted refractory metals and apparatusfor practicing the method. More particularly, the invention relates to aprocess for refining small compacts or bars by electron bombardment.

The peculiar problems attendant to refining refractory metals such astitanium, zirconium, molybdenum, tungsten, et al., have been attacked ina variety of ways. More recently it has been proposed that a source ofelectrons be directed towards a solid bar or compact of these moreactive metals in a high vacuum furnace. This particular approach topurifying refractory metals has met with great success since theelectron beam provides a source of heat which is both sharply selectiveand virtually free of contaminating influence.

An exemplary electron beam furnace for purifying a compact or solidstock in a continuous or semi-continuous manner .is disclosed andclaimed in Patent No. 2,880,483, issued April 7, 1959, to Hanks et al.In this embodiment of an electron beam-high vacuum furnace, the meltstock is suspended vertically and a cathode source of electrons iscaused to melt the lower end thereof which drips into a skull formed ontop of the resolidified melt supported by a water-cooled crucible. Thecast ingot, as the skull slowly solidifies from bottom to top iswithdrawn at the lower end of the furnace to provide the refinedrefractory metal.

One of the problems associated with such refining of melt stock orcompacts is that of forming the compacts or metal stock itself.Heretofore, in the prior art it has been necessary ordinarily toactually melt the refractory metal to form the stock to charge theelectron beam furnace. Alternatively, if a compact was desired, anextremely heavy hydraulic press had to be used to obtain the highpressures necessary to form it. For example, in many applications,hydraulic presses having capabilities of 20 to 40 tons per square inchare needed to form compacts sufficiently strong to support their ownweight (as required in a furnace such as that disclosed in the patentreferred to above).

The present invention overcomes this substantial disadvantage byproviding a method and apparatus which will work satisfactorily withloosely compacted powders, still provide a highly refined end product,and operate semicontinuously. The advantages of using loosely compactedbars of the raw material in an electron beam furnace are obvious. Theequipment necessary to lightly compact refractory metal powders is a farcry from that required to develop 20 to 40 tons per square inchpressure. As a consequence, the cost of forming the loose compacts usedin the present refining process represent a substantial saving.

Not only is the use of highly compressed bars expensive and wasteful ofequipment, but a further problem arises since the compacts have to bewelded together to form a continuous rod. Only in this way can theconsumable electrode in the furnace be supported vertically in anelectron furnace and, at the same time, be sufficiently dense to carrythe high currents that are necessary to refine the refractory metal. Thewelding of compacts or solid bars together requires more equipment andadditional expense, not to mention the more significant fact that itadds impurities to the melt stock. In order to minimize theseimpurities, it is usual practice to weld the compacts or solid barstogether in the presence of an inert atmosphere. Even so, someimpurities are added. As a result, to prepare the solid or compact stockfor furnaces of the prior art not only requires a substantial outlay inequipment and added expense, but results in a stock charge which isgenerally inferior.

It should not be inferred from the above that there are no existingtechniques available to refine granulated stock. On the contrary, thereare furnaces which are charged with granules of refractory metals. Thesehave been operated, however, in more or less non-continuous orbatch-type operations because of the problem of recharging furnaces,particularly ones wherein a high vac uum is maintained. Anotherdisadvantage attending the refining of metal from granular stock ismechanical grain movement. While these shifts of granules are not asharmful when pure metals are being refined, they are where alloys areinvolved. If the powder stock is alloyed, the grain movement can resultin an end product that is not of uniform quality and therefore illfitted for critical uses.

The present process and apparatus, which permits the use of relativelyloose compacts or stock, overcomes the grain movement problem incidentto alloy powder purification, the equipment expenses attributable tousing highly compacted or solid bars, and eliminates the necessity forwelding compacts together.

The present invention employs a fiat table or platform supported insidea high vacuum furnace to support two or more layers of alined,end-to-end oriented, loosely pressed compacts for movement in onedirection. Means are provided, operable from a point outside the vacuumchamber, to move these layers of pressed bars along the platform in theone direction, and a cathode is provided adjacent one set of ends of thepressed bars to heat and melt them by electron bombardment. A crucibleis provided in the furnace immediately beneath the ends of the pressedbars bombarded by the electrons. The crucible acts to hold a skull ofmolten metal in the top of the resolidified stock or to collect pelletsof the refined metal, as desired. Auxiliary cathode heating means may beprovided to maintain the skull in a molten state as the refined stock isslowly pulled from the lower side of the furnace.

Since the pressed bars are supported on a platform they do not need tosupport their own weight or for that matter to be integrally weldedtogether. The pushing rod for moving the compacts toward the end of theplatform where the electron source is operative is constructed so thatadjacent layers of pressed bars are staggered and no end of a compactoverlies the end of one on an adjacent layer. Thus, a small piece of abar on the lower layer is retained and prevented from falling into theskull prior to melting, in part, by the pressure of bars in the upperlayer. Conversely, the remains of an upper layer pressed bar isprevented from falling into the skull prior to being melted, in part,because of the support by a compact in the next lower layer. Thisstaggered superposition of the compacts overcomes the principaldisadvantage inherent in horizontally supporting and moving compacts.

Cooperating with the platform and external to the vacuum chamber ismeans mounted transverse to the normal movement of the pressed bars inthe one direction for restocking the platform whenever the bars thereonhave been substantially melted. In order to do this, the pusher fordisplacing the pressed bars toward the cathode heating source isretracted and the transverse member is caused tomove two or more newlayers of pressed bars in line with the path of the first pusher member.

By the use of equipment as described above and by employing smallcompacts, a good even rate of melting is obtained which not only lowersthe average D.-C. input to the cathode-anode heating circuit, butpermits the vacuum pump to remove gases in a more even manner. Thus,with such smaller compacts, the discontinuity in gas formation as pureor alloyed metals are refined is minimized and the overall vacuum can bemaintained at a more uniform figure without extreme variations.

Objects of the present invention, therefore, are to provide a method ofrefining refractory metals and apparatus for practicing the method whichutilize smaller and more loosely compacted charges and, as a consequencethereof, the apparatus is simpler in construction, more economical tooperate and provides a more highly refined product.

In accordance with one feature of the invention, the apparatus combinesa platform for supporting two or more layers of small loosely compactedcharges, means for maintaining the individual compacts of one layerdisplaced with respect to the ends of the compacts of the adjacentlayers, a source of electrons to heat and melt the charges, means tomove the layers adjacent the source of electrons in the overlappingrelation, and means to recharge the apparatus at times.

Another feature of the invention pertains to the combination in ahigh-vacuum furnace of a platform supporting member for two or morelayers of end-to-end oriented compacts, a source of electrons adjacentone end of the platform, means operable to displace the two or morelayers of pressed compacts towards the source of electrons inoverlapping relation, means for supporting the liquid stock adjacent thesource of electrons and means to recharge the furnace at times.

Yet another feature of the present invention pertains to the combinationof a platform supported in a furnace, two or more layers of looselycompacted charges laid end-to-end in each layer, a pushing rod tomaintain the ends of compacts in each layer in overlapping relation tothe ends of compacts in adjacent layers and to displace the layers as aunit towards one end of the platform, means adjacent the one end of theplatform for bombarding the ends of the compacts with electrons tothereby cause them to melt, a mold supported beneath the one end of theplatform to catch the molten charge, electron beam means for maintainingthe upper part of the material in the mold in a molten state, means formaintaining a high vacuum in the furnace, and means cooperating with theplatform to add layers of eompacts'intermediate the pusher rod and theone end of the platform as'needed.

Broadly, the present process for refining loosely compacted refractorymetals comprises the steps of supporting a plurality of compacts inend-to-end relation and in a plurality of layers, maintaining thecompacts in each layer overlapping the compacts in adjacent layers, andbombarding one set of ends of the compacts with an electron source tomelt the compacts.

More particularly, the process of the present invention might comprisethe steps of supporting pressed compacts of refractory metal powder in afurnace in end-to-end relation and in a plurality of layers, maintainingeach compact in each layer overlapping the compacts in adjacent layers,bombarding one set of ends of the compacts with a source of electrons toheat and melt them, displacing the plurality of layers of compacts intheir overlapping relation towards the source of electrons as the endsof the compacts melt, collecting the melted refractory metal, andrecharging the furnace with layers of compacts as needed.

These and other objects and features of the present invention may bemore fully understood when the following detailed description is readwith reference to the drawings in which:

FIG. 1 is a schemtaic representation of furnace and charging apparatusin accordance with the present invention;

FIG. 2 is a partial end view of the charging apparatus of FIG. 1;

FIG. 3 is a partial plan view of the charging apparatus of FIG. 1;

FIG. 4 is a partial schematic of the compacts adjacent the melting zonewhen a small part of a compact on an upper layer remains; and

FIG. 5 is a partial schematic of the compacts adjacent the melting zonewhen a small part of a compact on a lower layer remains.

Turning to FIGS. 1, 2 and 3, the apparatus for performing the instantprocess may be seen to comprise a high vacuum furnace 19 having awater-cooled platform 10 therein upon which is supported layers 1 and 2of loosely formed compacts of refractory material. A pushing member orpusher 11 is supported for movement along the surface of the horizonalplatform 10 through an external force (not shown). Its displacementalong a line (toward the right of the FIG. 1 drawing) causes the layers1 and 2 of the compacts to move towards the right in overlappingrelation. The overlap of the individual compacts 1a, 1b, 2a, 2b, etc.,is insured by the stepped surface on the forward (right) end of thepusher 11.

A circular cathode 12 is supported around the right end of the platform10 and the compact layers 1 and 2 and an annular focusing member 13cooperate therewith. The cathode 12 is focused to impinge upon the setof ends of the compacts adjacent the right end of the platform 10 inorder to melt the powdered compacts which are connected to a source ofpositive potential (not shown) to act as an anode for the cathode 12.

Immediately below the right set of ends of the compacts 1 and 2 isanother circular cathode 14 which cooperates with a focus and shieldmember 15. Below the cathode-shield combination 14-15 is a verticallydisposed water-cooled crucible 16.

With the compacts 1 and 2 constituting the anode of the cathode-anodeelectron beam circuit, the electrons flowing from cathode 12 cause theright set of ends of the compacts 1 and 2 to melt. The melt, in turn,drips into the uppermost part of the crucible 16 after passing throughthe cathode 14. The cathode 14 is focused by member 15 to impinge uponthe uppermost part of the solidified stock 18 supported in the crucible16 thereby to maintain a preselected size skull or molten pool 17 ofrefractory metal. As the molten metal continuously drips into the skull17 and solidifies, the stock 18 is withdrawn (by means not shown).

Since the pusher 11, the platform 10, cathodes 12 and 14 and thecrucible 16 are all contained in the high vacuum furnace 19, which ismaintained at a vacuum approximating one micron of mercury by action ofthe vacuum pump 20, relatively little or no contaminants are introducedinto the refining process as the compacts 1 and 2 are pushed into thepath of the electron flow from cathode 12. The stock 1, 2, etc., meltsand the refined bar stock 18 is withdrawn from the furnace as it does.

FIGS. 2 and 3 disclose the recharging mechanism for the refiningapparatus of FIG. 1* most clearly. Whenever the compacts 1 and 2 aresubstantially melted, the pusher 11 is moved towards the left side ofthe furnace of FIG. 1 and additional layers of loosely formed compacts1e and 20, for example, are propelled along the platform 10 in adirection transverse to the line of movement of. the pusher 11. Therecharging compacts 1c, 20 are moved in the line of movement of pusherrod 11 by a second pushing member 22 which is operated from a pointexternal to the vacuum chamber 19 (by means not shown) whenever thecompacts remaining become so small that the furnace requires recharging.

It Will be noted, particularly with reference to FIG. 3, that it isimmaterial whether or not the replacement charges 1c and 2c aredisplaced in overlapping relation originally since the stepped frontsurface 2'1 on the pusher 11 will cause them to overlap as they arepushed along towards the right side of the platform 10.

FIGS. 4 and 5 illustrate more clearly how the overlapping relation ofthe charging compacts 1a, 1b, 2a, 2b, etc., prevent small remainingpieces of a compact from prematurely falling into the skull 17. In FIG.4 there is illustrated a small remaining part of a compact 2b and, ascan be seen, it will not fall into the skull 17 due to the support ofthe lower compact 1b and the normal surface tension which exists betweenthe surfaces thereof and the adjacent compact 2a on its own layer andits supporting compact 1b. In the FIG. 5, the opposite situation isillustrated wherein the small piece of compact 1b remaining is on thelower level 1. Up until the last moment, this small portion 1b issupported intermediate compact 2a and the lip of the apron or platform10. Before it all melts the platform no longer supports it, however, thesurface tension between the contacting surfaces and the bond of moltenmetal flowing along its outer surface is sufficient to support it untilcathode 12 has completed the job of reducing it to liquid form.Naturally enough, the platform 10 cannot extend to the focus of theelectron beam because it would then be melted along with the compact.

It should be apparent that the present invention is not limited to twolayers of compacts. It can use two or more layers, provided the frontsurface 21 of pusher 11 is formed to insure the overlap of compacts inadjacent layers as they approach the bombardment area.

Rather than use a skull 17 to collect the refined metals for removalfrom the furnace 19, alternatively, the drops can be formed into pelletsfor further refining or mixing with other metals to obtain alloys, etc.The use of a skull 17 in a vertically movable melt stock 18 is purelyexemplary and should not limit the scope of the present invention.

Beyond this, while there are no specific means indicated for operatingthe pusher 11 or recharging pusher 22, it is apparent that these twocould be operated either manually or by automatic means. Further, it canbe seen that the pusher 22 can cooperate with the transverse part ofplatform 10 to provide a charging entrance for the vacuum furnace 19which does not interfere with the maintenance of the high vacuum insidethe furnace 19.

These and numerous other modifications can be made by those skilled inthe art without departing from the spirit and scope of the invention.Therefore, they are in no way intended to limit the scope of the presentdisclosure, which is only limited by the express language of theaccompanying claims.

What is claimed is:

1. A high-vacuum furnace for melting rectangular blocks of compactedgranular material arranged in a stack at least two layers deep, theblocks in each layer being aligned in an abutting end-to-endrelationship, comprising a flat, horizontal platform, arranged tosupport the stack of blocks with one end of said stack protruding overone end of said platform, at least one thermionic electron-emittingcathode, means for accelerating and directing electrons from saidcathode onto the protruding end of said stack acting as an anode to heatand melt the same, a crucible arranged under said projecting end toreceive the molten material dripping therefrom, means for moving saidstack lengthwise along said platform and including an externallyoperable pushing rod having an end thereof contacting the stack whichhas a stepped surface for maintaining individual blocks in adjacent layers of said stack in overlapping relationship to feed the protruding endof the stack into the electron bombardment zone as said end melts away,a vacuum container enclosing said platform, stack, cathode and crucible,and means for continually evacuating said container to a high vacuum.

2. A method of melting and casting granular material, which comprisescompacting said material into a plurality of similar rectangular blocks,placing said blocks on a platform within a vacuum tank and arrangingsaid blocks on said platform into a stack at least two layers deep, theblocks in each layer being aligned in an unconnected abutting end-to-endrelationship and the blocks in adjacent layers overlapping one anotherin unconnected relationship, evacuating said tank to maintain a pressurenot exceeding approximately one micron of mercury, moving said stacklengthwise along said platform until one end of the stack protrudes overone end of the platform, progressively melting away the protruding endof the stack by electron bombardment, progressively advancing the stackalong the platform to replace said protruding end as its melts away,catching the molten material in a crucible as it drips from saidprotruding end, continuously heating the molten material in the top ofsaid crucible by electron bombardment to maintain a molten pool thereof,continuously cooling said crucible to form a continuous solid ingotbeneath the molten pool at the top thereof, and continuously withdrawingsaid ingot from the bottom of said crucible to maintain a substantiallyconstant level of molten metal at the top thereof.

References Cited in the file of this patent UNITED STATES PATENTS1,069,326 Emberg et al Aug. 5, 1913 1,403,955 Hill Ian. 17, 19222,708,158 Smith May 10, 1955 2,762,856 Newcomb et a1. Sept. 11, 19562,880,483 Hanks et al. Apr. 7, 1959 2,963,530 Hanks et a1 Dec. 6, 1960

1. A HIGH-VACUUM FURNACE FOR MELTING RECTANGULAR BLOCKS OF COMPACTEDGRANULAR MATERIAL ARRANGED IN A STACK AT LEAST TWO LAYERS DEEP, THEBLOCKS IN EACH LAYER BEING ALIGNED IN AN ABUTTING END-TO-ENDRELATIONSHIP, COMPRISING A FLAT, HORIZONTAL PLATFORM, ARANGED TO SUPPORTTHE STACK OF BLOCKS WITH ONE END OF SAID STACK PROTRUDING OVER ONE ENDOF SAID PLATFORM, AT LEAST ONE THERIONIC ELECTRON-EMITTING CATHODE,MEANS FOR ACCELERATING AND DIRECTING ELECTRONS FORM SAID CATHODE ONTOTHE PROTRUDING END OF SAID STACK ACTING AS AN ANODE TO HEAT AND MELT THESAME, A CRUCIBLE ARRANGED UNDER SAID PROJECTING END TO RECEIVE THEMOLTEN MATERIAL DRIPPING THEREFROM, MEANS.